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THE CACTUS DESERT AT ZAPOTITLÁN
November 11, 1996

On Monday, November 11, with profound relief, I take a bus from Mexico City toward the southeast, to Tehuacán in Puebla State. I choose a window seat on the bus's right side so during the first part of the trip I can gaze at the gorgeous 5452-meter high (17,887 ft) volcano Popocatépetl issuing its steady plume of steam. Crossing the range from which Popocatépetl rises, at Río Frio, frost whitens the landscape. Doting fields along the road are picturesque teepees of machete-cut corn plants. It's a frost-killed, early winter scene, all gray and brown, and what a spectacle a lone Vermilion Flycatcher presents perching on an electrical line.

In Tehuacán I take a bus southwest to a place I've often visited but never was able to stay for long. Of all the spots on Earth I know, this has the greatest variety of succulents, particularly cacti, and I'm hoping the birds there will be spectacular, too. After climbing a good distance into a very rugged, arid and pretty landscape, late in the day I.disembark at Zapotitlán Salinas, usually just called Zapotitlán, near a roadside booth selling local onyx. The elevation here is about 1550 meters (5115 feet).

As the sun approaches the horizon, for about an hour I hike into the windswept desert not only looking for a good camping spot but also simply rejoicing in being back on the land. The cactus-filled landscape is a pure wonderland. A Phainopepla, a slender, crested, black bird, flashes white wing-patches as it darts about catching flying insects. How  alert-looking this bird is, gracefully cocking its head this way and that.

It's that unsettled time of the evening when the desert's boulders reradiate heat stored up all day, but the wind itself is getting chilly, and that wind is a stiff one. All around me rises a vast community of unbranched, columnar, Saguaro-like cacti rising as high as the rooftops of one-story houses, as shown at the right. Locally called Órganos, botanists know them as Cephalocereus hoppenstedtii. And here's something majestic: With the deep-shadowed, dark landscape behind them, these tall cacti appear as pale, greenish-gray, vertical streaks rising all around, and in the stiff wind they are all swaying together, as in a ghostly, rhythmic dance.

Finally I reach a small canyon with a silvery strand of water flowing through it. The canyon's walls rise only five or six stories high. A good arm could throw a rock from one canyon rim to the other. The stream averages only about a meter across (yard) but in this desert it's obviously a major presence, affecting life all around it. There's another  Vermilion Flycatcher atop a rock at water's edge. Several Rough-winged Swallows perform acrobatics above the stream. Turkey Vultures land to roost among the naked branches of a small tree at the canyon wall's summit. When they land they look very unsteady and for five to ten seconds keep their wings open as if balancing, and they close their wings circumspectly, as if expecting to tip over.

I want to camp next to the stream. However, the walls are steep and where the walls meet the stream's floodplain thorny mesquite and other bushes form impenetrable tangles . I follow several wildlife trails, but each peters out inside spiny brush where going with a backpack is impossible. Several times I retrace my steps and try again.

With barely enough light to see, one wildlife trail finally leads onto the canyon floor. Wind streams down the canyon, cold wind now, and when finally I get the tent pegged beneath a mesquite the small tree's feathery leaves rustle pleasantly, the stream trickles softly just a few steps away, crickets chirp from leaf litter all around the tree, and frogs croak from a nearby pool of water. There is no traffic rumble, and no neurotic Doberman Pinscher barking.

"Escaped once again, " I whisper into the wind.

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AN ECOLOGICAL ISLAND

The Zapotitlán desert is an ecological island in the sense that it is completely surrounded by non-desert biological communities. It occupies only a small section of the southeastern corner of Puebla State, and the northwestern corner of Oaxaca State. It owes its presence to the fact that right across the Tehuacán Valley to the east, the Eastern Sierra Madres rise high enough to block prevailing winds carrying moisture off the Gulf.

Similar to many oceanic islands, its inhabitants are often strange and unique. One of the most eye-catching is the Mexican Poneytail, Beaucarnea gracilis, shown at the right. Poneytails are sold as succulents in many North American garden shops, but the one sketched here has a trunk big as a full-sized refrigerator.

Botanist C.E. Smith Jr. writes that some 29 percent of the plant species found here are endemic -- found nowhere else on Earth. In fact, there are several endemic genera here. Some of those genus names look and sound wonderfully exotic: Oaxacania, Pringleochloa, Setchellanthus, Solisia...

I can't find literature about the birds. Who knows what I'll find here?

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ENSNARED

At dawn it's 8° C (47° F), and wind keeps streaming down the canyon. Soon the wind picks up even more and a strange rattling fills the air. It's yucca leaves knocking against one another.

As sunlight creeps down the canyon's slopes I wander in the chilly, blue twilight pooled along the stream bed. The meager stream is "braided," splitting and coalescing repeatedly, and sometimes on the downstream side of boulders there are tadpole-filled pools. The canyon's floor is an unvegetated bed of rounded boulders and cobblestones interspersed with long, flat-surfaced sandbars on which grow elephants'-eye-high willows and mesquite. It's hard to walk on the cobblestones, so as I hike along the stream I hopscotch from one sandbar to the other.

On one sandbar, suddenly I find myself ensnared by several sticky threads or filaments stretched across the trail. Because the strands are as strong as cheap sewing thread the idea that I've walked into a spider web is slow to form, yet, what else could they be?

Trying to back out of the mess, a dark blob the diameter of a doorknob and seemingly suspended in mid air draws before my face, and then a second blob descends from the opposite side. It takes a moment to focus on them, but, indeed, they are very large spiders, gorgeous things with legs banded yellow and black, and their bodies mostly black, with yellow and white spotting. They are similar to North America's Garden Spiders, of the genus Argiope.

But no Garden Spiders ever made webs like these. About thirty typical sheet webs the size of window fans, with spiders in the middle of them and suspended at various levels, are all spread against the wind streaming down the canyon. The open area in which the webs are strung is about 4.5 meters wide (fifteen feet), and the topmost web reaches some three meters high (ten feet). Passing vertically through the center of each web is a slender collection of sucked-dry husks of insect victims, now strung together with silk, like beads.

Some webs connect to one another but others stand apart. All, however, are interconnected through a sticky maze of tough threads of the type I wandered into. It's easy to visualize small birds becoming entrapped in this system, but there's no indication that this has happened.

Some spiders are smaller and more slender than others, so they are probably males. When a web is approached too closely, its spider so violently slings its body back and forth perpendicularly to the plane of the web that the web pulsates. A vagrant breeze bursts into the opening, the entire community of upset spiders begins bobbing, and the resulting multi-dimensional system of oscillating webs is psychedelic, disorienting, maybe even a bit threatening, and that's probably the object of the whole display.

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BIRDLIST #10

Here is this stop's Official List:

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THREE ENDEMIC BIRDS

Unlike the situation with plants, here I find no bird species endemic just to the Zapotitlán Desert. However, three species on the list are more broadly endemic to the highlands of southern Mexico north of the Isthmus of Tehuantepec. They are

• Gray-breasted Woodpecker
• Boucard's Wren
• Bridled Sparrow

The Gray-breasted Woodpecker is part of cluster of "zebra-backed" species very similar to eastern North America's common Red-bellied Woodpecker. Some ornithologists have lumped two or more of the species in the cluster together, but others insist that they are all separate. In other words, here evolution is at an in-between stage, where races are very well delimited, but it's debatable whether the races are species yet.

A similar case exists with the Boucard's Wren, which is an 18-cms-long bird (seven inches) very closely related to, and sometimes lumped with, the more widely distributed and more northern Spotted Wren, which we saw in the canyon at Bahuichivo. Both of these wrens are part of a cluster of species closely related to the Cactus Wren so common in the northern desert. In fact, some authors refer to the two wrens as the Boucard Cactus-wren and the Spotted Cactus-wren.

Of the three endemics, only the Bridled Sparrow is recognized even by the lumpers as a clearly distinct species. Still, it's obviously related to the Five-striped Sparrow of the Western Sierra Madres, and the Black-chested Sparrow of southwestern Mexico. These are all handsome, dark sparrows with heads boldly streaked with white.

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YELLOW GROSBEAK

In the above list one of the prettiest species is the Yellow Grosbeak sketched at the right, just as I saw him perched next to a bromeliad. This bird extends from western Mexico into Guatemala, and similar species (or maybe just subspecies...) are found as far south as Peru. Yellow Grosbeaks are found along forest borders, cut-over breaks, brushy woods and wooded canyons exactly like this in mountains and foothills. It's a little similar to North America's Evening Grosbeak, but that species has a much darker head and the white on its wing is much more extensive.

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SALT

In dazzling afternoon sunlight, during a hike downstream I come to a bend in the canyon where a clay cliff has been undercut by the stream so that it has collapsed. The resulting landslide has created a steep ramp leading from the stream bed, past the spiny mesquite belt along the stream, into the barren upland. I clamber up the incline and find a high spot for looking around.

Not far away, at the mouth of a small side-canyon, I'm astonished to see a cluster of about twenty interconnected, square, shallow ponds, each pond about five meters along the side (fifteen feet). Next to the ponds stand roofless, mostly collapsed ruins of several buildings.

The binoculars show that behind the ruins someone has cut into the steep slope creating a small vertical wall. A trail leads up to the wall where a regular wooden door is mounted on wooden beams. A room has been excavated inside the hill, and the door is its entrance. As I continue scanning the ponds, a jolting image floats into view --an old man wearing only white shorts and rubber boots, his shiny skin baked almost black by the sun. He's standing in the middle of a pond, looking exactly at me.

As soon as it's clear I've been seen, I step more clearly into view, wave, and begin walking deliberately toward the man. Up closer I read in the old man's face the fact that during the course of many years he has reached a state of equilibrium with his monotonous, difficult work. Patience and ability to endure hardship are plainly visible in his wrinkled face, as well as in his gazing-into-long-distance wrinkles. His tight-lipped mouth shows no hint of either a smile or a frown. His body is small, compact, and sinewy. I tell him I'm a gringo studying birds, and ask what the ponds are all about.

"Salt," he replies, with the expected economy of words. "We have saltwater springs up the canyon. We fill these ponds with their water, the water evaporates, and we get salt to sell."

Then he asks me how old I am, something many Mexican country-folk wonder about. Because it's such a frequent question, I've learned to make a game of it: I ask the old fellow to guess. Today, because I'm feeling supple and fit, I expect him to guess around thirty-five, though I'm almost fifty. He guesses sixty-five. Then I remember that in lands where people typically have such fine hair my balding head and graying beard throw people off. Then he asks me to guess his age.

"Sixty-five," is my honest opinion.

"Seventy-six," he smiles, and the smile shows that he knows he looks much younger.

"Hard work all my life," he explains, "never stopping. Never having much, just working... "

I can see he wants to get back to work, so we shake hands and I depart.

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FOSSILS

I had known that saline springs were in the area, but I didn't know where, and I didn't know they were still being used. In Zapotitlán's full name, "Zapotitlán de las Salinas," the word salinas means saltworks.

One of my books says that above us right now there's a mountain called Cuth, or Cerro de la Máscara (Hill of the Mask). At its peak rise pyramids built of rock and earth, and with ramps, stairs and roads connecting them. Ceramic pieces found there belong to Oaxaca's Monte Albán civilization, which peaked approximately 1,100 to 1,400 years ago.

During the hike back upstream, I rest next to a pool of water behind a boulder. In the gravel at my feet I notice a white cobblestone displaying an internal honeycomb structure. It's fossilized coelenterate coral. This reminds me that we are indeed in a limestone area, and that limestone often harbors fossils. I scoot closer to the limestone boulder next to me and look at it closely. Sure enough, embedded in its white matrix are dozens of spiraling outlines of snail-like gastropods about the size of a large toenail. The limestone in this area is Cretaceous in age, so these fossils lived maybe a hundred million years ago. Back then, South America was still joined with Africa, North America was hardly separated from Europe and Asia, and the part of the world these rocks come from was a shallow, warmwater sea.

Now the saltwater spring makes sense, too. It's easy to visualize a shallow coastal basin toward the end of the Cretaceous, as the Mexican landmass was rising from the sea. Over an enormous period of time saltwater flooded into the shallow basin, evaporated and left huge salt deposits which eventually were uplifted with the rest of the coast. Today rainwater falls onto the hills, seeps along subterranean fissures through the salt deposits, and issues from springs as saltwater with which the old man now fills his ponds.

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CACTUS DRINKING

On a hike through the hills above the canyon I walk through the forest of   Órganos. Next to a trail leading to the salt ponds a young cactus about my height has had its top half sliced off with a single powerful machete swipe. At first I assume that the damage is the usual mindless hacking of a bored traveler but farther down the trail I spot a couple of small wads of tough, fibrous material.

Somebody's been sucking water from cactus pith, and these wads are spit-out pith..

Back at the decapitated cactus, sure enough, at the edge of the clean machete cut someone has gouged out mouth-size chunks of white pith. With my knife, I do the same. The pith is tough. It's like carving Styrofoam.

But what a surprising amount of water the pith discharges as it's being chewed. It's cool, clean-tasting water, only slightly bitter. It's easy to see how, by chewing several such chunks, a big thirst could be quenched. The only inconvenience is that the pith is grainy and once the wad is spit out the mouth is left feeling gritty.

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SWALLOWS DAWN TO DUSK

In the canyon's bottom, around the campsite and along the stream, no bird is more conspicuous for most of every day than the Northern Rough-winged Swallow. Especially during the hours before dusk, six to eight wing up and down the stream, again and again, always softly calling their burry brrrtt brrrtt brrrtts.

These are plain little creatures, gray-brown on top and pale below. As often is the case with plain-looking beings, however, they enjoy a compensatory elegance: Their streamlined bodies could not more gracefully cut through the air. It is simply a delight to watch them.

In 1934, John A. Gillespie caught a male Rough-winged Swallow at its nest near Glenolden, Pennsylvania and took it by automobile to Milford, Delaware, 52 kilometers away (32.5 miles). Driving back immediately after releasing the bird, he arrived at the bird's Glenolden nesting place to find the bird already returned and helping its mate feed five young birds.

Some swallow species nest in such large colonies that when the young birds return home sometimes they wander into the wrong burrows. Adults of such communal species frequently reject strayed younglings and the young birds may die of starvation. In contrast, Northern Rough-winged Swallows are solitary nesters, and they don't discriminate between their own offspring and those of others placed in their nests.

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RANDOM PLEASURES

Soon after morning's sunlight breaks onto the canyon floor, a Red-tailed Hawk comes silently flying downstream at rooftop level. Right before reaching the campsite it veers to its right, lands atop a giant Órgano cactus, and perches there for a long time.

This is amazing, for the spines beneath the Red-tail poke straight up and are needle sharp. Apparently the hawk is like an Indian fakir on his bed of nails, benefiting from distributing his weight over a large number of spines. On the other hand, the hawk seems too heavy for the bed-of-nails phenomenon to work, especially because the spine tips themselves rise to irregular heights. To top it all off, the hawk could easily have chosen a dozen other nearby perches as well positioned as this one, and he seems to be showing absolutely no discomfort at all.

Later in the morning two Turkey Vultures land next to a pool of water a little downstream, clumsily hop and waddle across a few cobblestones to the pool's edge, and begin drinking in the manner of hens. They lower their heads to the water, level their heads somewhat so that water runs into their beaks, then raise their heads and point their beaks skyward, letting the water trickle down their throats. This is how most birds drink, but the vultures with their long, snaky necks look funnier doing it. Only a few bird species can pump or suck water with their throats -- mainly pigeons and doves.

Late in the afternoon a shadow silently slinks about inside an impenetrable fortress of waist-high agaves overgrown with vines. After failing to gain a view, and realizing that the bird is definitely evading me, I make the shhh-shhh-shhh "spishing" sound known to birders. The spishing does its job and what pops into view on an old agave flower stem rising above the bramble is a kind of bird uncommonly vulnerable to spishing, a wren. It's the endemic Boucard's Wren..

A Red-tailed Hawk atop an Órgano, vultures drinking like chickens, and an endemic wren who can't resist spishing... These are not Earth-shattering observations, but they are the kind that come along one after another during each day making my visit to Zapotitlán simply delicious.